Ceramic materials are an indispensable material in human life and modernization. It is one of the most important materials in inorganic non-metallic materials that people follow after metal materials and non-metal materials. It has the common advantages of metal materials and polymer materials, and its friability has been greatly improved in the process of continuous modification. Ceramic materials are unique in the field of materials because of their excellent performance. They are highly valued by people and will play a very important role in the future social development. Ceramic materials can be divided into two categories according to their properties and uses: structural ceramics and functional ceramics. Modern advanced ceramics have stable performance, high strength, high hardness, high temperature resistance, corrosion resistance, acid and alkali resistance, wear resistance, oxidation resistance, good optical properties, acoustic properties, electromagnetic properties, sensitivity and other properties far superior to metal materials. And high-molecular materials; and advanced ceramics are high-performance materials that have been manufactured through strict composition and production processes according to the required product properties, so they can be used in high temperature and corrosive media environments, and are the most active areas in the development of modern materials science. one. Here, the types of advanced ceramics and their application fields will be described in detail.
The excellent properties of its ceramic materials are high strength, high hardness, high modulus of elasticity, high temperature resistance, wear resistance, corrosion resistance, oxidation resistance, shock resistance, high thermal conductivity, low expansion coefficient, light weight, etc. Many fields have gradually replaced expensive ultra-high alloy steels or have been applied to areas in which metal materials are indispensable, such as engine cylinder liners, bushings, seals, and ceramic cutting tools. Structural ceramics can be divided into three categories: oxide ceramics, non-oxide ceramics, and ceramic-based composite materials.
1 oxide ceramic
The oxide ceramics mainly include magnesium oxide ceramics, alumina ceramics, cerium oxide ceramics, zirconia ceramics, tin oxide ceramics, silica ceramics, and mullite ceramics. The most prominent advantage of oxide ceramics is that there is no oxidation problem. Alumina ceramics have the characteristics of high mechanical strength and large insulation resistance, and can be used as vacuum devices, device porcelain, thick film and thin film circuit substrates, thyristor and solid circuit casings, spark plug insulators, and the like. Its strength and hardness are large, and it can be used as abrasives, textiles, and knives.
Magnesium oxide ceramics have good electrical insulation, are weakly alkaline substances, are hardly corroded by alkaline substances, and have strong corrosion resistance to alkaline metal slag. Many metals such as iron, nickel, uranium, thorium, molybdenum, magnesium, copper, and platinum do not interact with magnesium oxide. Therefore, the magnesia ceramic can be used as a crucible for melting metal, a mold for casting metal, a protective tube for a high temperature thermocouple, and a lining material for a high temperature furnace. Magnesium oxide absorbs moisture in the air and hydrates to form Mg(OH)2, which must be taken care of during the manufacturing process. In order to reduce moisture absorption, the calcination temperature should be appropriately increased, the particle size should be increased, and some additives such as TiO2 can also be added. Cerium oxide ceramic has a good thermal conductivity similar to that of metal, about 209.34W / (m · k), can be used as a heat sink; yttrium oxide ceramics also have good nuclear properties, strong neutron deceleration, can be used The decelerator and anti-radiation material of the atomic reactor; in addition, the high temperature and volume resistance of the atomic reactor can be used as a high-temperature insulating material; and its alkali resistance can be used for smelting rare metals and high-purity metals. , platinum, vanadium. Zirconium oxide ceramics have high refractoriness and low specific heat and thermal conductivity. They are ideal high-temperature insulating materials; they have good chemical stability and are resistant to acid and neutral substances at high temperatures.
2 non-oxide ceramics
Non-oxide ceramics include carbide ceramics, nitride ceramics, silicide ceramics, boride ceramics, and the like. Non-oxide ceramics, unlike oxide ceramics, have very little reserves in nature, require synthetic raw materials, and then are finished in a ceramic process. The standard free radicals of nitrides, carbides, and sulfides are generally larger than the corresponding oxides, indicating that the oxides formed are more stable. Therefore, oxides are easily formed during the synthesis of raw materials and ceramic sintering. The chemical bond between the oxide atoms is mainly an ionic bond, and the non-oxide is generally a covalent bond having a strong bond. Therefore, the non-oxide ceramic is refractory and difficult to sinter.
1) Silicon carbide ceramics have strong covalent bond properties, maintain high bond and strength at high temperature, have low strength reduction, and have small expansion coefficient and excellent corrosion resistance, and can be used as high-temperature structural parts. Due to its high melting point and high hardness, SiC ceramics are mainly used as super-hard materials, tool materials, wear-resistant materials and high-temperature structural materials. They can be used as heat-conducting materials and heat-generating materials because of their high thermal conductivity and low expansion coefficient. Silicon carbide ceramics are mainly used in the petroleum industry, chemical industry, automotive, aircraft, rocket, machinery mining, paper industry, heat treatment, nuclear industry, microelectronics industry, laser and other industries.
2) There are many types of nitride ceramics, including silicon nitride ceramics, aluminum nitride ceramics, boron nitride ceramics, and titanium nitride ceramics. Silicon nitride ceramics have high temperature resistance and wear resistance. They are used in ceramic engines for rotors, spindles and scrolls of gas turbines. They are widely used in metallurgy due to their good shock resistance, corrosion resistance, small friction coefficient and small thermal expansion coefficient. And in the thermal processing industry. The aluminum nitride ceramic can be used as a container for molten metal, a protective tube, or a vacuum vapor deposition container, and can also be used as a container for vapor-depositing Au in a vacuum, a heat-resistant transfer, and a heat-resistant jig. High electrical insulation resistance, excellent dielectric constant and low dielectric loss, good mechanical properties, corrosion resistance, strong light transmission, can be used as high temperature components, heat exchange materials, casting mold materials and non-oxidizing electric furnace according to the above characteristics. Furnace lining materials, etc.
Boron nitride ceramics are excellent in high temperature resistance and electrical insulation and can be used as insulation materials in the electrical industry. Since the thermal conductivity hardly changes with temperature and the penetration performance to microwave radiation, it can be used as a transmission window of the radar. Boron is present in boron nitride, so it has a strong neutron absorption capacity as a structural material for the atomic reactor. It is used as a high-temperature metal smelting crucible, refractory material, hot sheet and thermal conductive material, and has the advantages of high melting point, small thermal expansion coefficient and stable performance for almost all molten metals. It is the best material for manufacturing engine parts. Silicon nitride ceramics have high hardness, high melting point, good chemical stability and golden metallic luster. They are a good refractory and wear-resistant material, and they are decorative materials. In the machining industry, TiN coating on the tool can improve its wear resistance.
3 nano ceramic
Nano-ceramics, also known as nano-structured materials, are new materials developed in the 21st century. Its research is from the micro-composite to the nano-composite direction. The nano-ceramic material can not only bend like a metal material under low temperature conditions without cracking, but also can be mechanically machined like a metal material, or even a ceramic spring. . Nanoceramics can be used as protective materials, high temperature materials, artificial organ manufacturing, clinical applications, absorbent materials using silicon carbide as an absorbent, absorbent materials using ceramic powder as an absorbent, and piezoelectric properties. Its application areas are micro-coating, super filtration, adsorption, deodorization, catalyst, fixed oxygen, sensors, optical functional components, electromagnetic functional components and so on.
Ceramic matrix composite
A composite material is a material in which two or more substances having different chemical properties or different tissue phases are combined in a microscopic or macroscopic form. Ceramic matrix composites based on improved toughness can be divided into two categories: zirconia phase change toughening composites and ceramic fiber reinforced composites. Zirconium oxide transformation toughening composite is a high toughness material prepared by mixing part of zirconia powder with other ceramic powders. This material has been widely used in ceramic cutting tools.
Fiber reinforcement is considered to be the most effective and promising method for improving ceramic toughness. Fiber strength is generally much higher than that of the matrix, which has a strengthening effect on the matrix; at the same time, the fiber has a significant ability to hinder crack propagation, thereby increasing the toughness of the material. The most resilient ceramics today are fiber-reinforced composites. Another reinforcing material is ceramic whiskers. The whisker size is very small, but it is a nearly perfect fibrous single crystal. Its strength and modulus are close to the theoretical value of the material, which is very suitable for the strengthening of ceramics. Currently such materials are in ceramics. Cutting tools are widely used.
2. Functional ceramics
Functional ceramics are materials that primarily utilize their non-mechanical properties when applied, and such materials typically have one or more functions. Such as electrical, magnetic, optical, thermal, chemical, biological and other functions, as well as coupling functions, such as piezoelectric, magnetic pressure, thermoelectric, electro-optic, acousto-optic, magneto-optical and other functions. Functional ceramics have been widely used in energy development, space technology, electronic technology, sensing technology, laser technology, optoelectronic technology, infrared technology, biotechnology, environmental science and other fields.
1 electronic ceramic
Electronic ceramics include insulating ceramics, dielectric ceramics, ferroelectric ceramics, piezoelectric ceramics, pyroelectric ceramics, sensitive ceramics, magnetic materials, and conductive, superconducting ceramics. According to the dielectric properties of capacitor ceramics, they are divided into six categories: high-frequency temperature-compensated dielectric ceramics, high-frequency temperature-stable dielectric ceramics, low-frequency high-dielectric-type dielectric ceramics, semiconductor-type dielectric ceramics, and laminates. Capacitor ceramics, microwave dielectric ceramics. Among them, microwave dielectric ceramics have the characteristics of high dielectric constant, low dielectric loss and small resonance frequency coefficient, and are widely used in microwave communication, mobile communication, satellite communication, radio and television, radar and other fields.
2 thermal and optical functional ceramics
Heat-resistant ceramics, heat-insulating ceramics, and thermally conductive ceramics are the main applications of ceramics in thermals. Among them, the heat-resistant ceramics mainly include Al2O3, MgO, SiC, etc., because of their high temperature stability, they can be applied to the metallurgical industry and other industries as refractory materials. Insulating ceramics have excellent thermal insulation and are widely used in various fields.
Ceramic materials include optically absorbing ceramics, ceramic optical signal generators and optical fibers, which can be seen everywhere in life, such as paints and ceramic glazes. In the nuclear industry, the use of heavy ion ceramics such as lead and antimony to absorb and fix nuclear radiation waves is widely used in the treatment of nuclear waste. Ceramics are also important materials for solid-state laser generators, including ruby lasers and garnet lasers. Optical fiber is the main transmission medium of modern communication signals, and has better signal loss, high fidelity and large capacity than metal signal transmission lines. Transparent alumina ceramics are typical representatives of optical ceramics. In the manufacturing process of transparent alumina, the key is that the volumetric diffusion of alumina is the grain growth process of the sintering mechanism. Adding appropriate additives such as magnesium oxide to the raw materials can inhibit The growth of the grains. It can be used as a crucible for melting glass, an infrared detection window material, a lighting fixture, and can also be used to manufacture integrated circuit substrates in the electronics industry.
3 biological, antibacterial ceramics
Bioceramic materials can be divided into bio-inert ceramics and bio-active ceramics. In addition to measurement, diagnosis and treatment, bioceramics are mainly used as substitutes for bio-hard tissues, and can be applied to orthopedics, plastic surgery, oral surgery, and heart. Vascular surgery, ophthalmology and general surgery. Antibacterial materials are mainly used in household goods, household appliances, toys and other fields. Household appliances are one of the most widely used and widely used industries. In recent years, China's antibacterial materials industry has developed rapidly, and has been rapidly developed in the fields of industrialization and application development of inorganic antibacterial agents, organic antibacterial agents and photocatalytic antibacterial agents.
4 porous ceramics
Porous ceramics have the advantages of high light transmittance, large specific surface area, low density, low conductivity, high temperature resistance and corrosion resistance. They are used in automobile exhaust gas treatment, industrial sewage treatment, molten metal filtration, catalyst carrier, heat insulation and sound insulation materials. Wait. In recent years, the application of porous ceramics has expanded to the aerospace, electronics, medical materials and biological fields, which has attracted the attention of the global material industry and has been rapidly developed. In order to obtain different porous ceramics, various preparation methods have been successively proposed, such as adding a pore former, a sol-gel method, a hot pressing method, an ion exchange method, and the like.
In recent decades, the application and development of ceramic materials is very rapid. Ceramic materials are one of the most promising development materials after metal materials and polymer materials. Its comprehensive performance in all aspects is significantly better than the metals currently used. Materials and polymer materials. The application prospects of ceramic materials are still quite broad, especially the rapid development of energy, information, space technology and computer technology, which has further stimulated the application of materials with special properties. The preparation technology of advanced ceramic materials is changing with each passing day. The development of science and technology in the world is remarkable. The development of nano-ceramic materials has achieved amazing results and made major breakthroughs. It is believed that in the near future, ceramic materials will have better and faster development, demonstrating its important application value.